Abstract

Interlayer exchange coupling (IEC) in fully epitaxialtunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at . Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers.

The research at AIST was partly supported by Nanotech Challenge Project of the New Energy and Industrial Technology Development Organization (NEDO). The research at UNL was supported by NSF (Grants Nos. MRSEC DMR-0213808 and DMR-0203359) and the Nebraska Research Initiative.